1. Field of the Invention
The present invention is directed to a novel process for the preparation of 3-alkyl-cyclopentane-1,2-diones and in particular, to a novel process for the preparation of 3-alkyl-cyclopentane-1,2-diones via the intermediates 2-alkoxy-3,5-dicarboalkoxy-5-alkyl-cyclopent-2-ene- 1-ones by the condensation of esters of glutaric acid and oxalic acid in a polar aprotic solvent in the presence of an alkali metal alkoxide to form 3,5-dicarboalkoxy-cyclopentane-1,2-dione dialkali metal salts, alkylating said salts with an alkylating agent to form a 2-alkoxy-3,5-dicarboalkoxy-5-alkyl-cyclopent-2-ene-1-one, removing said solvent therefrom, and hydrolyzing the remainder to form a 3-alkyl-cyclopentane-1,2-dione. In particular, the invention contemplates the novel process defined above for the preparation of 3-methyl-cyclopentane-1,2-dione, also known as Maple Lactone, which finds immediate and practical utility as a flavoring agent in the manufacture of synthetic maple syrup.
2. Description of the Prior Art
It is generally recognized that 3-alkyl-cyclopentane-1,2-diones are materials having sweet characteristic flavors reminiscent of walnuts and which, heretofore, have been employed as flavoring additives in a variety of food products. In particular, 3-methyl-cyclopentane-1,2-dione is a white crystalline solid which has been found to be useful as the primary flavoring agent in the preparation of synthetic maple syrup and has come to be known as Maple Lactone.
Because of the well-accepted use of this product and its analogous compounds, the art has been interested in developing economical and commercial processes for the preparation of the 3-alkyl-cyclopentane-1,2-diones from readily available starting materials. However, the processes known heretofore in the patent and technical literature suffer serious technical deficiencies which render them unsuitable for development into economical, commercially feasible processes.
One such patent, which relates to products of this type, is U.S. Pat. No. 3,865,962 which teaches the preparation of these compounds by reaction of an alkyl acrylate with an alkali metal salt of an alkyl alkoxalylpropionate and decarboxylating the resulting cyclic compound. A further method is provided for preparation of analogous products in U.S. Pat. No. 3,652,643, specifically the preparation of 2-hydroxy-3-lower alkyl-cyclopent-2-en-1-ones by cyclization of dialkyladipate to 2-carbo-alkoxy-cyclopentan-1-one, alkylation thereof to 2-lower alkyl 2-carboalkoxycyclopentan-1-one, introducing an appropriate halogen gas into an anhydrous reaction inert organic solvent solution of said 2-lower alkyl-2-carboalkoxycyclopentan-1-one producing a product 2-lower alkyl-2 carbomethoxy-5,5-dibromo or dichloro cyclopentane-1-one, the acid hydrolysis of the latter compound to yield the final product.
In addition, U.S. Pat. No. 3,518,296 to Bucourt et al. teaches the preparation of 2-alkyl-cyclopentane-1,3 diones by the process of reacting a beta-keto ester with an alkaline cyclizing agent, saponifying the resultant 2-lower alkyl-4-carboxylate-cyclopentane-1,3-dione, decarboxylating the resultant 2-lower alkyl-4-carboxy-cyclopentane-1,3-dione, and recovering the 2-alkyl cyclopentane-1,3-diones.
Further, U.S. Pat. No. 3,349,130 also to Bucourt teaches a process for preparing the 2-alkyl-cyclopentane-1,3 diones which comprises cyclizing a lower alkyl ester of 5-lower alkyl-levulinic acid in the presence of an alkali metal tertiary alcoholate in an aprotic solvent to obtain a corresponding 2-lower alkyl cyclopentane-1,3-diones.
Another U.S. Pat. No. 3,671,589 teaches the preparation of 2-alkyl cyclopentane-1,3-dione by the reaction of succinic anhydride with an appropriate carboxylic acid anhydride in the presence of aluminum chloride and in an inert organic solvent. The acid hydrolysis of the latter product yields the final product. In addition, each of the above mentioned U.S. patents also disclose various other prior art processes for the preparation of compounds of this type.
None of the above processes, however, are considered to be particularly pertinent to the process of the instant invention.
Among the literature references which relate to the process of the instant invention are articles by Hesse et al., Liebig. Ann. 563, pp 31-53 (1949) and Gianturco et al., tetrahedron, 19, pp 2031-2049, (1963). Aside from the fact that the starting materials of the instant invention are mentioned by Gianturco et al. the similarity between the process of the instant invention and the processes mentioned by Hesse et al. and Gianturco et al. is remote.